Contrast control for photographic enlargers and printers



7 Jan. 14, 1947. A. SIMMON ETAL- 2,414,338

CONTRAST CONTROL FOR PHOTOGRAPHIC ENLARGERS AND PRINTERS FiledNOV. 9, 1945 5 Sheets-Sheet l A/fied S/mm n Lou/'5 L. Wwsg/ass INVENTORS BY M111 5 A TTOANE X Jan. 14, 1947. A. SIMMON' EI'AL I 2,414,338

CONTRAST CONTROL FOR PHOTOGRAPHIC ENLARGERS AND PRINTERS Filed Nov. 9, 1945 5 Sheets-Sheet. 2

Alfied 51/27/270 Lou/s L. We/sg/ass mmvrons BY Wm 5 Wm A TTORNE 3 Jan. 14, 1947. A. SIMMON EI'AL CONTRAST CONTROL FOR PHOTOGRAPHIC ENLARGERS 'AN D PRINTERS Filed Nov. 9, 4545 5 Sheets-Sheet 3 Alf/1d fijmman Lou/5L. Wezsg/ass l N V EN TORS A TTORNE K 0 l v a m Jill. 1-947- A. SIMMON EI'AL 2,414,338

CONTRAST CONTROL FOR PHO'ILOGRAPHIC ENLARGBRS AND PRINTERS Filed Nov. 9, 1945 5 Sheets-Shut 4 F v fi so 2 I: l

C ONTRAST SHORT YINIS l Lani mils I x $0 4 SECONN l Fly:

I Ahjred Simmer? Lou/5L. we/sg/ass mvzumns ham/m ATTORNEY- Jan. 14, 1947. A. SIMMON HAL 2,414,338

I CbNTRAST CONTROL FOR PHOTOGRAPHIC ENLARGERS AND PRINTERS Filed Nov. 9, 1945 5 Sheets-Sheet 5 Ffg: l3

7 I I III! 1/ ///I I III! l/l/l/l/ l g p 324 I z z e y K 330, a

[III/III,III/IIIIIIIIIIIII/IIIIIIIIIIIIIIIIII'IIIIIIIIIIIIIIIIIIII U// I/ l/ I/lI/l/ll/ ll/l/l I,

/IIIlI/IIlIl//IIII. I III/ll! Alfred Sing/nan .Lou/s' L. We/sg/ass mmvrons mat/ I ATTORNEY /I/IIIIIIIIIIIIIIIlII/IIIIII/IIIIIIIIIII mandolin. 14, 1947 coiv'rnas'r CONTROL FOR rno'roomrmc moans AND rmn'rms ,Alfred Simmon, Jackson Heights, and Louis L.

Wcisglass, New York, N. Y.,

assignors to Simmon Brothers, Inc., Long Island City, N; Y., a corporation of New York Application November 9, i945, Serial No. cameo 12 Claims.

A light sensitive paper has recently been developed' which is capable of delivering prints of photographic negatives in any degree of contrast from extremely hard to extremely soft depending upon the wavelength of the light to which it is being exposed. With blue light'a very high degree of contrast is obtained, while with yellow light the gradation is very soft. Intermediate degrees oi contrast can be obtained by exposing the paper subsequently to light of either color, the contrast in this case depending upon the ratio of the blue exposure time to the "yellow exposure time; The use of this paper, therefore, necessitates, first, an estimate oi the total necessary exposure time, depending upon the density of the photographic negative, and second, a division of this exposure time into two suitable portions for the "blue and yellow exposure,

respectively, depending upon the gradation of the negative, and, finally, a double exposure with the two proper exposure times through a blue and yellow filter, respectively. It is the purpose of this invention to provide mechanical and electrical means to this end.

The contrast control device consists of three principal parts, i. e., the enlarger or printer proper, which comprises a source of light, a color changing device and a timing device.

In the drawings in which a typical enlarger is shown equipped with a preferred form of a 30 color changing device comprising two color filters and a timing device,

Fig. 1 is a side view of the whole'assembly, partly in section Fig. 2 is a horizontal sectional ,viewof the 35 filter shifting device along the plane of line 2-2 in Fig. l. in one position, and

Fig. 3 is a similar sectional view in another position;

Fig. 4 is another color changing device em-= bodied in the lamp housing of the projector carriage of another type of enlarger; r

Fig. 5 is a partial cross sectional view along the plane of line t-5 in Fig. 4,"

' Fig. 6 is a horizontal sectional view through the 45 timing device shown in Fig. l, but drawn in a larger scale;

Fig. 7 is a vertical sectional view along the plane of line 7-7? in Fig. 6;

Fig. 8 is an electric circuit diagram applicable to the timing device; I

Fig. 9 is another modified electric circuit diagram applicable to the same device:

Fig. 10 is an elevational view of a modified timing device:

I proper comprises a Fig. 11 is a cross sectional view along the plane of line ii-ii in Fig 10;

Fig. 12 is a cross sectional view along the plane of line l2-l2 in Fig. 10;

Fig. 13 is a longitudinal sectional view along the plane of line it-JIS in Fig. 11; and

Fig. 14 is a longitudinal sectional the plane of line kid-id in Fig. 11.

Like characters of reference denote similar parts throughout the several views and the following specification.

The general principle 01 this invention is illustrated in Fig. l which shows a photographic enlarger, a filter shifting device, and an automatic time switch which controls the total exposure time; as well as the proportionate share of the two color filters. As shown, the latter adjustment is arbitrarily divided into divisions, determining view along the contrast of the print.

It will be understood that the enlarger shown in this drawing is merely a typical example and that enlargers of other designs, as well as contact printers, can be equally well used with this invention.

The enlarger shown in this instance consists of a baseboard ii on which a suitable bracket 22 is mounted. Fastened to this bracket are U channels 23 on which a projector carriage 2% slides. This movement is facilitated by rollers 25, and the weight of the entire projector assembly is counter-balanced by a spring 28. The projector lampihousing ll, containing an incandescent lamp 228 and a double condenser 29. Immediately under the condenser is positioned a holder it for the photographic negative. A lens 3i projects an enlargedimage of the negative onto the baseboard 2B which, during exposure, supports the light sensitive paper. The lens 3! is mounted on a lens carrier 32, the position of which can be adjusted vertically with respect to the negative it by means of a friction drive 33. This drive is actuated by the operator until a sharp image of the photographic negative appears in the plane of the sensitive or bromide paper on the baseboard. The lens carrier is connected to the filmholder 38 by means of a flexlble but light-tight bellows 35. It will beunderstood that up to this point the enlarger as described is quite conventional.

In front of the lens is shown a color filter assembly 35, and this assembly is shown in detail in Figs. 2 and 3. This assembly is similar to one described in application Serial #540,590, filed by us on June 16, 1944, now Patent Number 2,399,-

577, issued April 30, 1946. It consists oi apivoted plate so which supports a yellow filter 3i! and a blue filter so. The plate 88 can perform a rotary motion around pivot 39 which is secured to a stationarybase plate 38 fastened to theabove mentioned lens carrier 32. Mounted upon this base plate is is a solenoid 8i which'by means of a connecting rod 3s, engages plate Stat a point 59. A spring 5i is provided holding the filter support so ordinarily in the position shown in Fig. 2. As soon as solenoid ll is energized, it moves the connecting rod to and thereby rotates the filter support at so that it now assumes a position shown in Fig. 3. it is'understood that theforce of the solenoid is considerably stronger than the forceof spring 5i. It will be clear that with this arrangement, yellow filter 37 is in front of the lens as long as the solenoid is not energized, and blue filter so is in front of the lens as soon as current is supplied to solenoid 3!.

This electrically operated filter changing device can, of course, be'widely modified. For example, it may be advantageous to use a small torque motor instead of a magnet since this. is less liable to introduce vibrations. It may also be advisable to position the filter assembly not immediately in front of the lens, but between the lens and the negative, or between-the negative and the condenser, or between the lamp and the condenser. The filter carrier 36 may also, instead of a rotary motion, perform a straight .line sliding motion. Modifications of this nature, which are obvious to anybody skilled in the art, fall, of course, within the scope of this invention.

A different form of color control device can'be used in connection with enlargers broadly disclosed in the three co-pending' applications Serial I #577,216, #609,873 and #614=,208 filed by Louis L. Weisglass, one of the co-inventors herein.

The projector assembly of such enlargers comprises a conventional enlarging lens and a conventional condenser, but the source of light is a diffusely reflecting surface disposed substantially in the focal point of this condenser and illuminated by a spotlight. Compared to the conventional arrangement in said focal point of a lamp with an opal vessel and emitting diffused light, this arrangement offers a much better utilization of the available light and permits the application of much higher wattages than heretofore possible. For a detailed description of the general principle involved and for a discussion of the gains in efficiency and'light output, we wish to refer to the co-pending application Serial #577,216.

A color control device applicable to this type of enlarger is shown in Figs. 4 and 5, showing the lamp housing part of the projector assembly only. This lamp housing consists of the main housing 830, the condenser with the condenser housing m and the condenser lenses I32. the two spotlights use and the colored reflector assembly. v

Two reflectors W and lfil are provided which are mounted on opposite sides of a supporting plate 52. This supporting plate is fastened to a shaft I63 which terminates in a spur gear I64. The entire assembly is mounted in a housing led and a small motor I368 is provided which, by means of another spur gear 61 drives the aforementioned gear ltd. The motor IE8 is of the type which may be stalled for prolonged periods of time without overheating and which is com-' monly called "torque motor. The rotation of the supporting plate 562 is confined to 180 by means of a fixed stop its and a stop pin its on gear Hit, and a spring, its is provided which returns the reflector assembly to its original position as soon as the motor its is de-energized. An arrangement of this type can very advantageously be used in connection with a variable contrast paper of the varigam type. For example, the

two reflector plates its and iti may be of a yellow reflectors its and iti. This rotation will come to a stop after 180 when the stop pin its comes in contact with the stop 58. From now on the reflector plate lei, which originally was in the upper or inactive position, will now be in the lower position, and the balance of the exposure will, therefore, be given by the color determined by therefiector plate 665. After the exposure is finished the motor its is disconnected, whereupon spring llfi'returns the entire reflector plate assembly to its original position.

A timing device is shown in Figs. 6 and '7. Its outstanding characteristic is its faculty to control not only theexposure time, but independentthereof the two relative percentages of the two respective color exposures. The timing device comprises a housing 2M to which all parts are mounted and from which two control knobs 2G2 and 203 protrude. As can be seen from Fig. l, knob 202 controls the contrast and cooperates with a dial calibrated in 100 parts indicatin percentages of exposure to one color, exposure to the other color, of course, being equal to balance'of 100%. Knob 203 controls the total exposure time and cooperates with a dial which is shown starting with 5 and ending with 55 seconds. I

This arrangement is merely chosen by way of example and any other range may be obtained if so desired. On top of the housing is a Push button 296 by means of which the operator can initiate an exposure cycle. Mounted within housing it! is a peculiarly shaped bracket'265 on which all component parts are mounted. This bracket has two ends with holes which are adapted to be fastened'to corresponding lugs attached to housing 2M. As can be seen, bracket 205 comprises a straight center portion, the purpose of which will be explained later,' and various lugs to which various. shafts, gears and wheels can be ,55 mounted.

The main part of the time switch isv apivoted lever 2%. This lever is adapted to perform a rotary motion covering a relatively small angle during an exposure cycle. The lever is shown in its starting position and is again shown in dotted lines in an intermediate and in its final position. These positions are called 206' andfldt" respectively. This lever may be rotated by any convenient kind of motive power, but it is, of course, preferable to use a small synchronous electric motor of the type used for electric clocks.

These motors are commercially avaiiable with a built-in speed reducing gear train of any desired ratio and with a magnetically operated gear shift 7 which automatically engages and disengages the gear train when the motor is energized and deenergized. The drive shaft is then free to be returned tothe starting position by suitable means such as a spring or by gravity. A motor of this type is shown in Figs. 6 and 7 as 2st. Its outtherewith the supporting plate 962 with the two a a aa put shalt 108 carries a spiral shaped cam 20!.

This spiral shaped cam is in operative contact with the aforementioned lever 208. The motor upon being energized turns in a counterclockwise direction indicated by the arrow, and thereby drives lever 205. The timeswitch is built on the principle that lever Z08 always travels the same angular distance, but at a difierent and adjustable rate oi speed. This rate of speed can be adjusted in any convenient manner and we have merely shown one of the simplest in which the speed change is effected by shifting motor 201 either to the right or to the left in a direction parallel to the starting position of lever 208. Motor 201 is mounted on a bracket 201a which slides on 'the'aforementioned straight portion of bracket 205. This sliding motion may again be effected in any convenient manner and merely, as a typical Pulley 2m then is connected to the aioremen-q tioned knob 203 and it will be clear that rotation of knob 203 moves bracket 201a on the straight portion of bracket2ll5 thereby changin; also the position of motor 201 and spiral cam 209 with respect to lever 206. Obviously, if the motor is pushed far to the left, only a small angle of rotation of cam 209 is needed in order to push lever 206 from this starting position as shown 'in solid lines to its end position 2%" as shown in-dotted lines, and, therefore, the time elapsing between these two extreme positions becomes quite short. On the other hand, if motor 2M and cam 2% are pushed for to the right, substantially a full revolution of the cam will be required in order to shift the lever 206 between its two extreme limits. The exposure time then will be as long as possible.

A switch is arranged within the housing in such a manner that it is actuated by lever 20% at the end of its rotary travel. This lever must have lock-in characteristics, 1. e., it must stay in its new position even after the removalof the actuating force and not automatically by spring force or other means return to its original position. sition a special resetting device must be provided by means of which the entire cycle of operations can be stopped. A switch of this type is known as a switch of the maintained contact" type and is shown in Fig. 7 diagrammatically as MS. Switches of this type are commercially known as micro-switches and are available in this maintained contact type with a resetting device actu'ated by the aforementioned push button 2M.

not need a resetting device, such as indicated by 7 push button 2M, but an independent push button will be provided by means of which the operator can initiate an exposure cycle. This arrangement is not shown in Figs. 6 and 7 but a circuit 15 travel.

In order to return it to its original po- '5 shuts oi! the light of the enlarger or printer as soon as lever. 205 reaches the position 208" making contact with switch 2 It. A second switch 2 II is provided to actuate the color changing device. Y

' This color changing device must be actuated 1 sooner or later depending upon the type of contrast that the operator wishes to obtain. There-,

fore, the position of switch 2 is adjustable in .such a way that it will come in contact with the main lever 206 sooner or later during it rotary The mechanical arrangement by means oi which this adjustment is being made is not important and merely by way of an example we have shown switch 2 mounted on a bracket M which is connected to a gear segment 2i6. This gear segment, in turn, is actuated by a spur gear 2H which is attached to the aforementioned knob 202. Obviously, turning knob 202 in a clockwise direction will turn lever ass in a counter-clockwise direction and will, thereby, raise switch tit gradually increasing the percentage of the first color exposure until it reaches 100%. In the same manner turning knob 202 and gear 2H in a counter-clockwise direction will turn switch supporting lever 255 in a clockwise direction so thereby lowering switch 2 i t and eventually bringing it into a position in which the first color ex-.

posure becomes 0%. Switch 2 may also be of the so-called micro-switch type but no lock-in characteristics are required and the switch will be of the so-called "momentary contact type.

As stated before, two alternate circuit diagrams of the time switch are shown in Figs. 8 and 9. Fig. 8 makes use of a relay to sup ly the required lock-in characteristics for switch 21s.

49 The switch M3 is in this case a simple switch of the momentary contact type with normally closed (NC) contacts. It is in series with a relay coil 22c and a normally open (N0) push button iii. The relay is equipped with two independent '5 sets of normally open (NO) contacts 222 and 223.

m. n is immaterial whether switch m is normally open or normally closed, the only difierence being that in one case the first color will be exposed flrst and second color later, whereas in the other case, the first color will be exposed later and the second color first.

The circuit diagram of Fig. '9 shows an alternate circuit which makes use of a switch of the maintained contact" type, thereby dispensing with the relay. Switch did is normally closed and of the maintainedcontactf type, being equipped with a push button 208 by means of which it can be reset. This switch controlsthree parallel circuits, one containing motor 292, the second lamp 228 and the third solenoid iii and switch 2M,

which again may be either normally open or normally closed, but which must be of the momentary contact" type without having any of the lock-in characteristics. Instead of solenoid M for the color changing device, the motor I68 oi garages the device shown in Figs. 4 and 5 may, of course, be used.

The working function or the device may be fully understood from these drawings and circuit diagrams. In the case of Fig. 8, the operator momentarily actuates the push buttons and closes contacts 22 i; This energizes relay coil 220 thereby-closing the two pairs of contacts 222 and 223.

Since contacts 222 are now closed, the relay remains energized after the operator relinquishes push button 225. Therefore, the three branch circuits depending upon contacts 223 remain energized, i. e., the lamp lights up and the motor starts running thereby rotating lever 203. At

, some point of its travel, lever 263 comes in contact with switch 2 as which we may assume to be tor 207-, upon being de-energized, automatically disengage its gear shift and permitslever 206 to drop back into its starting position. Lamp 28 becomes currentless, thereby terminating the exposure.

The circuit in Fig. 9 works in a very similar way. The switch M3 is here of the maintained contact type and, while it is of the normally closed type, its contact at the-beginning of an exposure will be open, having remained so from the previous exposure. The operator by pushing the resetting button 222 restores its original position, i. e., closes it. This energizes motor 221 and lamp 28 but not as yet solenoids! if we assume switch 2M. to be of the normally open type. As soon as lever 206 reaches switch 2M it closes it, thereby energizing solenoid it! and actuating the color changing device. Lever 206 continues to rotate until it meetsswitch 2H3, thereby opening the circuit again which now, since this switch is ofthe maintained contact type remains open. Motor 201 again disengages its gear shift and permits lever 206 to drop into its starting position, and lamp 28 becomes currentless, thereby terminating the exposure. 0

Another modification of the timing device is shown in Figs. 10 and 14. This modification employs the same basic principle as, but is somewhat different in detail from, the structure shown inFigs. 6 and '7. The chief structural difierence is that instead of shifting the motor withthe spiral cam as a unit, the motor remains stationary and drives a shaft of square cross section. The spiral cam is equipped with a hub with a correspondingly square hole and is slidably mounted on the square shaft. This modification lends itself particularly well to a timer design with two different timing ranges, since it is very easy to use one motor on either end of the square shaft. These motors are equipped with reduction gears of different ratios, and it ispreferable to have one motor run ten times as fast as the other one, so that two ranges with a ratio of 1:10 can be obtained.

The timer comprises a housing 30! within which all component parts have been mounted. The front panel has two slots and two straight scales, one for the contrast and one for the time. A movable slide is' provided within each slot and v 3 these slides are actuated by knobs 302 and 363 respectively. On top of the timer is again a push button 363 which actuates the resetting device of the micro-switch 3l3 which is again of the maintained contact" type. A pivoted lever 306 is rotatably mounted within the housing and supports a long cylindrical roller 320 the purpose of which will be explained later. The-lever 303 has a projection 32! which at the end of the rotary travel of said lever comes in operative contact with the micro-switch 393. Two motors 333i and 30? are mounted on brackets 3th and 390, and drive a square shaft 363. This shaft does not necessarily have to be square, but may be triangular or round with a keywa'y or the like. in the appended claims this shaftis called polyg onal and it will be understood that obvious modifications of this cross section shall b construed to fall within this definition. The two motors 301 and 301' are of the same type described above, i. e., of the synchronous type and equipped'with magnetic gear engaging means. The built-in reduction gears of both motors shall, of course, be of different ratios so that the operator may select one of two speed ranges. Since the motors are arranged opposite each other as shown, one must rotate in a clockwise and the other in a counter-clockwise direction.

Mounted on shaft 306 is a spiral shaft cam 303 which is now equipped with a hub 322. The outer periphery of cam 309 is in contact with the aforementioned long cylindrical roller 320. It has been found that the presence of this roller very effectively minimizes friction between cam and lever 306. The hub 322 has a square hole and the cam assembly can, therefore, slide on the square shaft 308;. This is done by shifting knob 303. Attached to knob 303 is a connecting piece 323 which terminates in a fork which engages the hub 322.

A second micro-switch 3M of the momentary contact type, as distinguished from the maintained contact type described above, is arranged in such a manner that it will be actuated sooner or later by lever 306 during its rotary travel. Exactly as described above, the first switch 313 controls the illumination of the enlarger, terminating it after lever 306 has finished its stroke, whereas the second switch 3M controls the color shift and is being actuated sooner or later during the stroke of lever 306. The instance of this actuation depends upon the position of switch 3 which can be adjusted in the following manner: Inspection of Fig. 13 discloses that switch 3 is mounted on a pivoted lever '3l5, The right end of this lever is urged upwardly by a spring 324. Approximately in the middle of this lever i a small roller 325 which makes contact with a straight cam 326. This cam 326 is, in turn, connected to knob 302 by a connecting member 321. It will be clear that, if knob 302 is moved to the right or to the left, cam 326 will be moved likewise thereby depressing roller 325 and with it lever 3 I 5 or permitting both to rise. This, in turn. changes the position of switch 3M and thereby the instant by which the rotary lever 306 will actuate it during its stroke. This is accomplished by a cam-like projection 330, shown in Figs. 12 and 13, which is connected to lever 306 by a conneoting piece 33L, A small switch 332, Fig. 10,

permits the operator to energize selectively either motor 307 or 30'! thereby using one of the two amasse It is obvious that various other changes in form,

proportion and minor details of construction may be resorted to without departing from the principle or sacrificing any of the advantages of the invention as defined in the appended claims.

What we claim as new is:

1. A contrast control device for photographic enlargers and printers, comprising a source of light, a color changing device and a timing device, said timing device comprising a pivoted lever, means to rotate said lever, means to adjust the speed of rotation of said lever, a first switch controllingsaid color changing device and adapted to be actuated by said lever during its rotation, means to adjust the position of said first switch relative to said lever whereby said switch may be actuated sooner or later during the rotary travel of said lever, and a second switch controlling said source of light and adapted to be actuated by said lever at the end of its travel, whereby said source of light is being shut ofi'.

2. A contrast control device according to claim 1, the angle of rotation of said lever being less than 30.

3. A contrast control device according to claim 1, said means to rotate said lever comprising an electric motor with a built-in speed reducing gear train and a magnetically operated gear shift which automatically engages the gear train when said motor is energized, and means to return said lever to its initial position as soon as said motor is de-energized and said gear train disengaged.

4. A contrast'control devic for photographic enlargers and printers, comprising a source of light, a colorchanging device and a timing def vice, said timing device comprising a pivoted lever, means to rotate said lever, means to adjust the speed of rotation of said lever, a first switch controlling said color changing device and adapted to be actuated by said lever during its rotation, means to adjust the position of said first switch relative to said lever whereby said switch may be actuated sooner or later during the rotary travel of said lever, and a second switch controlling said source of lightand-adapted to be ac tuated by said lever at the end of its travel,

whereby said source of light is being shut off, said means to rotate said lever comprising an electric motor, a spiral shaped cam in operative contact with said lever, and a reduction gear driven by said motor and driving said cam.

5. A contrast control device according to claim 4, said means to adjust the speed of rotation of said lever comprising means to shift said motor with its reduction gear and cam in a direction parallel to the initial position of said lever.

6. A contrast control device according to claim 4, said means to rotate said lever including a shaft of polygonal cross section driven by said motor, the axis of said shaft being parallel to said lever in its initial position, and said cam having a. hub with a correspondingly polygonal hole and being slidably mounted on said shaft, said means to adjust the speed of rotation of said lever com= prising means to slide said cam on said shaft.

7. A contrast control device according to claim 1, said means to rotate said lever including a polygonal shaft, the axis of said shaft being parit allel to said lever in its initial position, two motors with reduction gears of difierent ratios mounted on opposite ends of said shaft, respectively, and adapted to drive said shaft at difierent rates of speed, a spiral shaped cam with a hub with a correspondingly polygonal hole mounted slidably on said shaft, and said means to adjust the speed of rotation of said lever comprising switching means to energize selectively one of said motors and means to' slide said cam on said shaft.

8. A contrast control device according to claim 1, said first switch being of the momentary contact type, its contacts returning to their initial position after the removal of the actuating force,

I device according to claim 1, comprising said second switch in series with a circuit composed of three parallel branches, said second switch having a pair of normally open contacts, and being of the maintained contact type, its contacts remaining in their new position after the removal of the actuating force, the first of said branches containing a motor driving said rotating lever, the second of said branches containing a lamp, constituting said source of light, and the third of said branches containing electromagnetic mean actuating said color changing device, in series with said first switch.

10. The electric circuit for a. contrast control device according to claim 1, comprising arelay with its coil in series with said second switch and with a push-button, said second switch having a pair of normally closed contacts, and said push-- button having a pair of normally open contacts, said relay actuating two pairs of normally open contacts, the first pair of said contacts being connected to the corresponding contacts of said push-button, thereby forming a lock-in switch for said relay, the second pair of said contacts being in series with a cir,uit with three parallel branches, a motor driving said rotating lever in the first branch, a lamp constituting said source of light in said second branch, and electro-magnetic means actuating said color changing device, in series with said first switch, in the third branch.

11. A contrast control device according to claim 1, said color changing device comprising two filters oi difierent colors and electromagnetic means to shift one or the other of said filters into a position between said source of light and a sheet oi sensitized material on which a print is being made.

12. A contrast control device according to claim '1, said color changing device comprising two refiectors of different color and electromagnetic means to shift one or the other of said reflectors into a position where it reflects light coming from said source onto a sheet of sensitized material on which a print is being made.

' ALFRED SIMMON.

hours a wmsGLAss. 

